Cells and Organelles

Question 1

What are cells?

Answer 1

Fundamental units of life;
Semi independent within the body;
Contain mechanisms for growth, metabolism and replication by division

Question 2

What are organelles?

Answer 2

Subunits of cells; have a defined structure and perform specific activities. Some are membrane bound (unlike ribosomes) allowing for a specialised environment (e.g pH) within the organelle which is different to that of the cell.

Question 3

Tissue

Answer 3

Organised assembly of cells within the body and their extracellular products.
Carry out similar and coordinated activities.

Question 4

Organ

Answer 4

Assembly of tissues coordinated to perform specific functions in the body.

Question 5

System

Answer 5

Assembly of organs with specific, related activities sharing regulatory influences; or diffuse functional network of cells situated in many parts of the body

Question 6

Prokaryote

Answer 6

Single celled organism in which its DNA in a circular strand, lies free in the cytoplasm; no membrane bound organelles.

Question 7

Eukaryote

Answer 7

Uni-/multi-cellular organism in which DNA lies in linear chromosomes in the nucleus; has cytoplasmic, membrane bound organelles

Question 8

Virus

Answer 8

Assemblage of nucleic acids (either RNA or DNA); parasitic on either eukaryotes or prokaryotes; subvert protein to make more viruses, which then escape and make viruses.

Question 9

What are the types of electron microscope and how do they work?

Answer 9

Transmission electron microscope: looks at cell surface, reflects electrons off heavy metal coating (Au)
Scanning electron microscope: looks inside a cell, electrons pass through the sample.

Question 10

What is the factor that affects the maximum size of a cell?

Answer 10

Surface area to volume ratio as diffusion is only efficient over a distance of less that 50 um. Distance between nucleus and periphery of cell needs to allow for efficient diffusion.

Question 11

How can a cell overcome its size limiting factor?

Answer 11

Having thin processes which can help direct the movement of substances around the cell via the cytoskeleton; having gap junctions between cells allows for the movement of substances between the cells; having more than one site for gene expression.

Question 12

What protein filaments make up the cytoskeleton of a cell?

Answer 12

Actin (the thinnest one, found in muscle)
Microtubules (thickest, pulls daughter cells apart)
Intermediate filaments (provide mechanical strength of the cell)

Question 13

What does the cytoskeleton of the cell regulate?

Answer 13

The shape of the cell, and it guides and drives the movement of substances around the cell.

Question 14

What is the approx. size of a nucleus?

Answer 14

3-10 um

Question 15

How is DNA organised within a eukaryote?

Answer 15

DNA wound around histones (nucleosomes)

Nucleosomes + non-histone proteins = chromatin

Question 16

Nucleolus

Answer 16

Where rRNA is transcribed and ribosome subunits assembled.

Question 17

RER

Answer 17

Has ribosomes on cytoplasmic face of membrane, site of synthesis of proteins for export. Vesicles budded from RER and are transported to Golgi, then are excreted.

Question 18

SER

Answer 18

Biosynthesis of membrane lipids + steroids

Start of N-linked glycosylation and detoxification of xenobiotics

Question 19

Peroxisomes

Answer 19

Contains enzymes that synthesise and catabolise H2O2; synthesis of phospholipids (plasmalogens) and detoxification.
Oxidation of VLCFA’s happens here too.

Question 20

Approx size of peroxisome

Answer 20

0.5-1.5 um

Question 21

Golgi

Answer 21

Protein sorting office; involved in modification of proteins:
O-linked glycosylation of carbohydrates and lipids.
Synthesis of lysosomes

Question 22

Approx size of mitochondria

Answer 22

0.5-2um